Cellulose is a linear polysaccharide of glucose residues connected by β-1,4 linkages. It is the main component of plant cell walls, and the basic building block for many textiles and for paper. It gives plant cells remarkable strength helping them to resist mechanical stress and osmotic pressure. Cotton is the purest natural form of cellulose.
Cellulases or cellulolytic enzymes are a group of glycoside hydrolase enzymes that catalyze the hydrolysis of beta-1,4 glycosidic linkages in the cellulose polymer. Cellulases are known to be produced by a large number of bacteria, yeast, and fungi. Cellulases comprise a catalytic domain/core (CD) expressing cellulase activity. In addition to the catalytic domain, the cellulase molecule may comprise one or more cellulose binding domains (CBDs), also named as carbohydrate binding domains/modules (CBD/CBM). The CBD enhances the binding of the enzyme to a cellulose-containing fiber and increases the efficacy of the catalytic domain.
Cellulases are utilized, based on their properties, in various industrial fields. In the textile industry, cellulases are used in denim finishing for creating a fashionable stone washed appearance in denim cloths in a biostoning process, and they are also used, for instance, to clean fuzz and prevent formation of pills on the surface of cotton garments. In detergent industry, cellulases are used to brighten colors, to prevent graying and pilling of garments and to improve cleaning. Cellulases are further used in food industry, including baking, and animal feed manufacturing, and they have a great potential in the pulp and paper industry, for instance, in deinking to release ink from fiber surfaces, in improving pulp drainage and fiber modification, in energy reduction, in refining and drying stages of paper, board and pulp production. Cellulases are also utilized in hydrolysis of lignocellulosic material for, e.g. bioethanol production.
The practical use of cellulases is hampered by the nature of the cellulase compositions, which often are enzyme mixtures having a variety of activities and substrate specificities. The unique properties of each cellulase make some more suitable for certain purposes than others. The wide spectrum of industrial uses for cellulases has established a need for commercial cellulase products containing different cellulase components and functioning in different pH and temperature ranges. The production costs of microbiologically produced enzymes are tightly connected with the productivity of the enzyme producing strain and the final activity yield in the fermentation broth. There exists a need in the art to identify enzyme variants and enzymatic compositions that have improved efficacy and capacity to act on a greater variety of cellulosic materials.
US2011250674 (A1) provides a method for improving the properties of a cellulolytic enzyme i.e., an endo-1,4-glucanase, by amino acid substitution, deletion or insertion. The invention discloses Humicola insolens cellulase variants, which have been improved with respect to activity; and/or sensitivity to anionic tensides; and/or pH optimum and pH profile as well as stability. US20130244292 relates to a family 5 glycoside hydrolase variant having endoglucanase activity and to polynucleotides encoding the polypeptides.
Although cellulolytic enzymes have been used successfully in commercial applications for many years, a need still exists for new cellulolytic enzymes with altered properties, such as improved performance, in varying industrial applications.